Risk Factors for Instrumentation Failure After Total En Bloc Spondylectomy of Thoracic and Lumbar Spine Tumors Using Titanium Mesh Cage for Anterior Reconstruction

Journal Pre-proof Risk factors for instrumentation failure after total en bloc spondylectomy of thoracic and lumbar spine tumors using titanium mesh cage for anterior reconstruction Zhehuang Li, MD, Feng Wei, MD, Zhongjun Liu, MD, Xiaoguang Liu, MD, Liang Jiang, MD, Miao Yu, MD, Nanfang Xu, MD, Fengliang Wu, MD, Lei Dang, MD, Hua Zhou, MD, Zihe Li, MD PII:

S1878-8750(19)32895-5

DOI:

https://doi.org/10.1016/j.wneu.2019.11.057

Reference:

WNEU 13726

To appear in:

World Neurosurgery

Received Date: 10 September 2019 Revised Date:

10 November 2019

Accepted Date: 11 November 2019

Please cite this article as: Li Z, Wei F, Liu Z, Liu X, Jiang L, Yu M, Xu N, Wu F, Dang L, Zhou H, Li Z, Risk factors for instrumentation failure after total en bloc spondylectomy of thoracic and lumbar spine tumors using titanium mesh cage for anterior reconstruction, World Neurosurgery (2019), doi: https:// doi.org/10.1016/j.wneu.2019.11.057. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.

Risk factors for instrumentation failure after total en bloc spondylectomy of thoracic and lumbar spine tumors using titanium mesh cage for anterior reconstruction

Zhehuang Li, MD, Feng Wei, MD, Zhongjun Liu, MD, Xiaoguang Liu, MD, Liang Jiang, MD, Miao Yu, MD, Nanfang Xu, MD, Fengliang Wu, MD, Lei Dang, MD, Hua Zhou, MD, Zihe Li, MD

Department of Orthopedics, Peking University Third Hospital, Beijing 100191

Corresponding Authors’ name and current institution:

Zhongjun Liu, MD and Feng Wei, MD Department of Orthopedics Peking University Third Hospital, Beijing 100191, China Corresponding Authors’ Email: Email for Zhongjun Liu: [email protected] Emai for Feng Wei: [email protected]

Key Words: spinal neoplasms; total en bloc spondylectomy; nonfusion; instrumentation failure; revision surgery; risk factors Short title: IF after TES using TMC

Risk factors for instrumentation failure after total en bloc spondylectomy of thoracic and lumbar spine tumors using titanium mesh cage for anterior reconstruction

Abstract Objective: This study aimed to investigate the risk factors for instrumentation failure (IF) after total en bloc spondylectomy (TES) of thoracic and lumbar spine tumors using titanium mesh cage (TMC) for anterior reconstruction. Methods: Data of patients who underwent TES for thoracic and lumbar spine tumors in our institution were retrospectively reviewed. Anterior reconstruction was performed using TMC filled with morcelized allograft or morcelized autograft. Posterior reconstruction was performed using pedicle fixation. Survival analysis of the time from TES to IF was conducted. Kaplan-Meier method was used for univariate analysis. Factors of statistical significance were subjected to multivariate analysis by Cox regression analysis. Results: In total, 30 patients (20 men and 10 women), with a mean age of 37.1±14.3 (range, 14-65) years were included. The mean follow-up period was 41.8±21.3 (range, 13-120) months. Bone fusion was achieved in 23 (76.7%) cases. IF occurred in 8 cases. The mean time from TES to the first IF was 31.8±15.1 (range, 13-64) months. On univariable analysis, body mass index (BMI) >28, perioperative radiotherapy, and TMC in oblique position were found to be associated with IF. On multivariable analysis, these three factors entered into the Cox regression model were also

significant. Conclusion: Total en bloc spondylectomy is able to achieve durable oncological control. However, instrumentation failure, a not uncommon late complication that leads to reoperation should be caused concern. Perioperative radiotherapy, titanium mesh cage in the oblique position, and BMI>28 are significant predictive factors.

Introduction

Total en bloc spondylectomy (TES) is a surgical procedure designed to achieve complete resection of a vertebral tumor as well as to provide an adequate tumor margin.1-3 It has been reported to decrease the local recurrence rate and prolong survival in appropriately selected patients.4-8 The operation completely removes the entire vertebral body and surrounding ligament structure, resulting in severe instability of the spine. For patients indicated for TES for tumor resection, robust spinal reconstruction with strong internal fixation to achieve solid osseous fusion is needed to restore the integrity and stability of the resection site and maintain spine function. Fusion rates varied from 36.0% to 100.0% for spinal fusion following resection of spinal column tumors.9 Instrumentation failure (IF) after en bloc resection is not uncommon complication, and its occurrence rate varied from 0% to 40%.7, 10-15 Nevertheless, most previous studies briefly mentioned IF when describing complications and focused more on oncology-related prognosis. Moreover, relatively few articles have focused on this issue and conducted in-depth analysis. Thus, in this

study, we aimed to report the clinical outcome of spinal reconstruction after TES of thoracic and lumbar spine tumors using titanium mesh cage (TMC) for anterior reconstruction in our institution and examine the risk factors for IF.

Methods

Patient sample

From December 2009 to April 2017, 52 consecutive patients with primary or metastatic spinal tumors underwent TES in our center, and their data were retrospectively reviewed in this study. Our inclusion criteria were as follows: (1) at least 24 months of radiographic follow-up after surgery, (2) ambulatory at follow-up with or without assistance, and (3) TMC filled with morcelized bone graft used for anterior reconstruction. The exclusion criteria were as follows: (1) cervical spine or sacrum involvement, (2) sagittal resection of the vertebra, and (3) reconstruction method applied that was not able to achieve solid bone fusion. Patient characteristics including sex, age, body mass index (BMI), and neurologic function; tumor-specific data including pathology, location, tumor extension, treatment history, and imaging studies; and treatment-related data including surgical procedure, preoperative embolization, and adjuvant therapy were reviewed and collected from the electronic medical records and Picture Archiving and Communicating System. This retrospective study was approved by the institutional review board of our hospital.

Treatments

The preoperative histology diagnosis was based on computed tomography (CT)-guided biopsy in all cases. X-ray, CT, and magnetic resonance imaging (MRI) were routinely performed for preoperative tumor evaluation. For tumors located close to great vascular structure, CT angiography was also performed. Positron-emission CT was performed for metastatic tumors to exclude systematic metastasis. A posterior-only approach was preferred when it was technically practical. When the tumor was located in the lower lumbar spine, there was involvement of surrounding structures that were not safely reachable posteriorly, or there was a huge paravertebral extension of the tumor, a combined approach was performed. TES consists of two steps, that is, en bloc resection of the posterior element and en bloc resection of the anterior column as described previously.1 If any surrounding structures were involved in the tumor, a partial or full resection was undertaken with the help of another specialist surgeon. Anterior reconstruction was performed using TMC filled with morcelized autograft harvested from the iliac crest or rib; if the volume was insufficient, morcelized allograft was mixed in. Posterior reconstruction was conducted through the pedicle screws, rods (diameter 6.0 mm), and transverse connectors. The posterior instrumentation was adjusted to slightly compress the inserted cage. No bone morphogenetic protein was used. The wound was soaked in distilled water for 2.5 min followed by highly concentrated cisplatinum (0.5 mg/ml) for 2.5 min after tumor removal in each stage of the procedures. Perioperative adjuvant therapy was performed according to the decision of a

multidisciplinary working group. A minimum interval of 4 weeks between preoperative or postoperative radiotherapy and surgery was recommended. In all cases, a rigid spinal brace was used for a postoperative period of at least 3 months.

Postoperative Evaluation

Follow-up protocol included a follow-up visit and X-ray imaging, computed tomography (CT), and magnetic resonance imaging (MRI) every 3 months for the first year, every 6 months for the second year, and yearly thereafter. Given the huge land area of our country and medical insurance reimbursement and referral policy, it is difficult for some patients to complete the follow-up protocol exactly as planned; thus, telephone follow-ups were done to make up for this, but radiological images would not be available. In this study, for instrumentation survival analysis, the follow-up time was only calculated to the date of the last radiographic follow-up in our institution. CT scan with multiplanar reconstructions was used for bone fusion evaluation in every case. We consider that bone fusion was achieved when mature bony trabeculae that bridged across the cage between the adjacent upper and lower endplates without radiolucent line were observed. Segment height was defined as the distance between the midpoint of the upper endplate of the cranial body above the TES site and the midpoint of the lower endplate of the caudal body below the TES site on midsagittal reconstructive CT scan (Figure 3). TMC subsidence was defined as the loss of segment height by comparing the immediate postoperative and the last follow-up

segment height. TMC oblique was defined as a mismatch of >10° can be observed between the endplate (or osteotomy plane) and the TMC on immediate postoperative midsagittal and midcoronal reconstructive CT scan (Figure 3). IF includes rod fracture, screw broken/loosened/back-out, and cage displacement.

Statistical Analysis

The survival analysis of the instrumentation was conducted. Time zero was defined as the time TES was completed, and patients were followed until the occurrence of the first IF or the date of the last follow-up visit with radiological images available. For univariate analysis, the Kaplan-Meier method was used, and survival curves were compared using log-rank test. Factors significant at the P <0.05 level in the univariate analysis were included in the Cox proportional hazards multivariate model, and a backward selection based on the Wald statistic was performed. In all analyses, a value of P <0.05 was considered statistically significant. Data were analyzed using SPSS software version 19.0 (SPSS Inc., Chicago, IL). In this study, junctional regions include T1-T2, T11-L1, and L5.16

Results

After implementing the inclusion and exclusion criteria, 30 patients were included in this study (Figure 1 and Figure 2). The population comprised 20 men and 10 women, with a mean age of 37.1±14.3 (range, 14-65) years. Of these patients, 23

were admitted for primary spinal tumors, and the histologic diagnoses were aneurysmal bone cyst (n=1), Ewing sarcoma (n=1), giant cell tumor (n=14), hemangioendothelioma (n=2), osteoblastoma (n=2), and osteosarcoma (n=3). Seven patients were admitted for metastatic spinal tumors. The primary location was the thyroid in two cases, breast in two cases, and colon, lung, and kidney in one case. There were 21 cases with tumors located in the thoracic spine and 9 cases with tumors located in the lumbar spine. Three patients were previously admitted in other hospitals for surgery. The mean radiographic follow-up period was 41.8±21.3 (range, 13-120) months. Recurrence was found in two patients, and metastasis was found in three patients. A single posterior approach was adopted in 24 patients; in other six patients, a combined anterior and posterior approach was used. Single-level TES was performed in 25 cases, two-level in four cases, and three-level in one case. TMCs were filled with morcelized autograft in 24 cases and with morcelized autograft and allograft in six cases. Anterior fixation was performed in four cases. No strut graft was used. Two patients received preoperative radiotherapy, seven patients received postoperative radiotherapy, one patient received both.

IF cases and revision surgery

Bone fusion was achieved in 23 cases, and the overall fusion rate was 76.7%. All seven patients with nonfusion experienced IF during the follow-up, and another IF occurred in a case with bone fusion 29 months after the surgery. For the eight patients who experienced IF (Tables 1 and 2), the mean time from TES to the first IF was

31.8±15.1 (range, 13-64) months. All eight IFs manifested as rod fracture including double-rod breakage in five cases (one with loosened screw) and single-rod breakage in three cases. All rod breakage was located between the rod and the first screw below the fusion segment. Seven patients with nonfusion complained of severe mechanical pain when IF occurred. However, the other patient with fusion was asymptomatic, and the IF was found during routine radiographic follow-up. No neurological deterioration was observed in any of the cases. The average TMC subsidence distance was 10.9±4.0 mm at the time of IF. Revision surgery was performed in six cases. Two patients did not undergo revision surgery because of personal reason. No evidence of local recurrence was found on preoperative evaluation, and the intraoperative histological results were all negative. Rod(s) replacement and abnormal curvature correction were performed in all cases. Satellite rods were also used in four cases. Two patients underwent repeat revision surgeries due to repeated rod breakage.

Risk factors analysis for IF

The results of univariable analysis on the prognostic factors affecting IF are shown in Table 3. In our study, BMI>28 (P=0.011), perioperative radiotherapy (P=0.005), and TMC in the oblique position (P=0.004) were found to be associated with IF. On multivariable analysis, the three factors entered into the Cox regression model were also found to be significant (Table 4). The hazard ratio (HR) of IF was

8.07 for patients with BMI >28 (95% confidence interval [CI] 1.55-41.90, P=0.013), 9.86 for patients with perioperative radiotherapy (95% CI 1.61-60.40, P=0.013), and 7.60 for patients with TMC in the oblique position (95% CI 1.35-42.83, P=0.022). Figure 4 shows the Kaplan-Meier curve for time to IF among all study patients, the estimated IF-free survival rates were 89.9% at 24 months and 69.6% at 60 months. Figure 5 shows the Kaplan-Meier curve for time to IF stratified by perioperative radiotherapy. Figure 6 shows the Kaplan-Meier curve for time to IF stratified by TMC position. Figure 7 shows the Kaplan-Meier curve for time to IF stratified by BMI.

Discussion

In this study, we present the outcome of spinal reconstruction after TES of thoracic and lumbar spine tumors using TMC for anterior reconstruction by reviewing a sample of 30 patients in our institution. Based on our analysis, we found that perioperative radiotherapy, TMC in the oblique position, and BMI>28 are the risk factors for IF. TES, reported by Tomita in 1990s,3, 17 is a surgical procedure aimed at achieving complete resection of a spine tumor with an adequate tumor margin in the treatment of spinal tumors. It has been commonly accepted and applied in the treatment of spinal neoplasms because of its favorable and encouraging outcomes, especially for primary aggressive, malignant, and solitary metastatic lesion in the thoracic and lumbar spine.4, 8, 18, 19 Moreover, with the development of novel adjunctive treatment

options, the overall survival of patients with spinal column tumors has been increasing.20-22 Thus, durable spinal reconstruction should be taken into consideration to improve long-term quality of life of the patients.23 Reconstruction of segmental defects after en bloc resection is a challenging and debated topic. Various reconstructive techniques were used for anterior column reconstruction. There is gross variability from surgeon to surgeon and from center to center, but limited evidence exists on which method is superior to another.13 Achieving long-term stability is a challenge in all reconstruction selections. Given the interstudy heterogeneity, fusion rates varied from 36.0% to 100.0% for spinal fusion following resection of spinal column tumors,9 and the IF rate after spondylectomy ranges from 0% to 40%.4,

9-11, 13, 14

Cages packed with morcelized allograft or

autograft were commonly selected by surgeons for anterior reconstruction after vertebrectomies.9, 13 However, evidence on reconstruction outcome using cages after en bloc spondylectomy with analysis of risk factors related to IF is relatively insufficient. To our knowledge, only three studies10,

14, 15

conducted a risk factor

analysis for IF after TES. In these studies, TMC was the most commonly used option for anterior structural support, but patients using other methods like expandable cage, polymethylmethacrylate block, and strut bone graft were also included. In these studies, history of radiotherapy, number of instrumented vertebrae, cage subsidence, and TES at the lumbar level were the risk factors. Fusion status was only evaluated in one study15 for the patients with IF. In our study, the overall fusion rate was 76.7%, and the overall failure rate was

26.7% in a mean follow-up of 31.8 months after the surgery. Previous studies showed that most of the IFs occurred in the posterior system.11 In our study, all IFs manifested as rod breakage. Moreover, in this study, not all patients with IF complained of back pain, suggesting that comprehensive imaging studies are important during follow-up visit. No neurological deterioration was observed, suggesting that it may not be catastrophic. Park et al.15 performed CT on 12 patients who experienced IF after TES, and nonfusion was only found in four patients. However, in our study, 7 of the 8 patients who experienced IF were found to have nonfusion. Based on our study, we hold the opinion that achieving solid bone fusion was the vital key of maintaining long-term stability for spinal reconstruction. When pseudoarthrosis existed, IF will be inevitable in long-term survival due to metal fatigue caused by repeated fretting.24 Perioperative radiotherapy serves as a commonly used adjunctive therapy for the treatment of spine tumors. Unfortunately, it has been proved to be a risk factor for IF after en bloc spondylectomy.10, 14, 15 Despite the direct suppression on fusion process of the bone graft caused by ionizing radiation, the adverse effect on the bone quality of the adjacent vertebra25,

26

may also increase the risk of construct subsidence.

Besides, radiotherapy may lead to muscle atrophy and weakness, reducing spine stability.27,

28

Treatment paradigms using evidence-based approaches that address

immediate and long-term outcomes, with careful monitoring of the patients’ quality of life through the course of their disease, must be developed. Radiotherapy should only be used after careful treatment planning, and indiscriminate irradiation must be avoided. In our series, all patients received conventional external beam radiotherapy.

Harel et al.29 found that postoperative stereotactic spine radiosurgery results in lower rates of IF and higher rates of fusion compared with conventional fractionated radiation. They thought that radiosurgery limits the treatment dose to the tumor so that the fusion area can be partially spared. TMC placed in an oblique, rather than upright, orientation would result in primary instability and excessive point loading by a portion of the cage rim on the endplate, leading to TMC subsidence, unstable, and eventual failure of the construct.30-32 In this study, TMC in the oblique position was defined as a mismatch of >10° between the endplate (or osteotomy plane) and the TMC. The angle was proved capable of leading to cage subsidence in biomechanical study.32 Given the limited number of available angles at the ends for the “off-the-shelf” TMC, it is sometimes difficult to match with the non-parallel endplates (between the defect when regional kyphosis, scoliosis, and local deformity imposed by pathological fracture existed). TMC selection and placement require care of surgeons. IF may also occur in fusion cases15; even if the anterior graft seems to be fused on radiographic examination, the fusion mass may be not strong enough to endure long-term repetitive force, causing fatigue fracture of rods.15 In our study, rod fracture occurred in one case with fusion (in a 21-year-old woman with a BMI of 32.9). In our study, BMI>28 was shown to be related to IF. Overweight patients gave more load stress on the prosthesis and challenge more on the stability of the spinal reconstruction. Generally, posterior reconstruction with at least two vertebral levels above and

below is recommended,13 though some studies suggested that a longer posterior fixation may improve the stability and reduce the risk of failure.10, 11 However, in this study, we did not find that a longer posterior fixation was able to reduce the risk of IF. Bias may exist because surgeons will choose long-segment fixations when high risk factors exist. However, it was also suggested that we do not have to blindly and routinely extend the posterior fixation, and it should be performed based on patient-specific issues (i.e., region of reconstruction, bone quality, postoperative therapy, general conditions that may impair bone formation capacity). In our study, we found that subsidence was a common phenomenon in anterior reconstruction after TES according to CT evaluation. Mild subsidence has no consequences on posterior instrumentation, while severe subsidence subjects posterior instrumentation to a higher biomechanical stress when the load on the anterior column decreased. Matsumoto et al.10 found that cage subsidence >5 mm is a risk factor for IF. In our study, TMC subsidence in the non-IF group was 2.9±2.6 mm, while in the IF group, the TMC subsidence was 10.9±4.5 mm (P<0.001). However, for the risk factor analysis, we hold the opinion that subsidence was not a preexisting factor but an endstage manifestation of IF related to many other reasons, such as nonfusion, TMC position, and endplate condition. Thus, it was not included in the statistical analysis in our study. However, the obvious relation between subsidence and reconstruction failure may help us understand more about the development process of IF and provide some clues for future improvement in reconstruction technology.33 This study had several limitations. All patients come from a single center, which

may limit the generalizability of our finding. Because of the retrospective nature of the study, data collected from the medical records and their analysis may be limited. Although we have a sample of 30 cases and a mean follow-up of 37.1 months, a larger sample achieved by a multicenter study and longer follow-up are still necessary. We hope that through our study we can reveal the risk factors leading to nonfusion and IF after TES and attract the attention of surgeons.

Conclusions

Total en bloc spondylectomy is able to achieve durable oncological control of the disease. However, instrumentation failure, a not uncommon late complication that leads to reoperation should be caused concern. Although the failure often occurred in the posterior system, solid bone fusion in the anterior construct is extremely important to long-term stability for spinal reconstruction. Perioperative radiotherapy, titanium mesh cage in the oblique position, and BMI>28 are significant predictive factors for instrumentation failure. These factors suggest that a durable reconstruction is a complex issue that involved reconstruction technology, adjuvant therapy, and patient-ralated factor.

Figure Legends

Fig. 1. Details of the 30 patients underwent TES. Fig. 2. Histology of the 30 patients underwent TES. Fig. 3. Segment height was defined as the distance between the midpoint of the upper endplate of the cranial body above the total en bloc spondylectomy (TES) site and the midpoint of the lower endplate of the caudal body below the TES site on midsagittal reconstructive CT scan (the yellow line). Titanium mesh cage (TMC) oblique was defined as a mismatch of >10° can be observed between the endplate (or osteotomy plane) and the TMC measured on immediate postoperative midsagittal and midcoronal reconstructive CT scan (the green lines).

Fig. 4. Kaplan-Meier curve for time to IF among all patients in the study. IF, instrumentation failure

Fig. 5. Kaplan-Meier curve for time to IF for patients with or without perioperative radiotherapy. IF, instrumentation failure

Fig. 5. Kaplan-Meier curve for time to IF for patients with upright TMC position or oblique TMC position. IF, instrumentation failure; TMC, titanium mesh cage

Fig. 6. Kaplan-Meier curve for time to IF for patients with BMI≤28 or BMI 28. BMI, body mass index; IF, instrumentation failure

Fig. 7. Representative case: in a 50-year-old male patient, 2 years after nephrectomy, the isolated L3 metastasis was shown on CT and MRI (A and B). TES of L3 was performed using a posterior-only approach. Cage with morcellized allograft was used for anterior reconstruction. Angular mismatch between the endplate and the cage can be observed (C). Rod breakage occurred 27 months after the surgery, and severe cage subsidence can be observed (D). Revision surgery was performed to change the rods; another two satellite rods were also used (E and F).

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TABLE 1 Details of the 8 cases with instrumentation failure No.

Sex

Age

Histology

Involved segment

Approach

Instrumented levels

Adjuvant therapy

1

Male

37

Giant cell tumor

T12

Posterior

2 above and below

Postoperative radiotherapy

2

Male

42

Hemangioendothelioma

T2

Posterior

2 above and below

None

3

Male

39

Giant cell tumor

T1-T2

Posterior

3 above and below

Preoperative radiotherapy

4

Male

23

Giant cell tumor

L1

Posterior

2 above and below

Postoperative radiotherapy

5

Female

35

Osteoblastoma

L1

Posterior

2 above and below

None

6

Male

50

Renal cell carcinoma met

L3

Posterior

2 above and 3 below

Postoperative radiotherapy and targeted therapy

7

Male

35

Osteoblastoma

T12

Posterior

2 above and below

None

8

Female

21

Hemangioendothelioma

T9

Posterior

2 above and below

Postoperative radiotherapy

TABLE 2 Details of the 8 cases with instrumentation failure (continued) No.

Instrumentation survival

Symptom

time (mos)

TMC

Fusion

subsidence(mm)

status

Failure detail

Revision surgery

1

50

Pain

10.6

Nonfusion

Double rods breakage

Rods replacement

2

13

Pain

7.6

Nonfusion

Single rod breakage

Without revision

3

17

Pain

15.2

Nonfusion

Double rods breakage

Rods replacement, satellite rods assistance

4

24

Pain

11.5

Nonfusion

Double rods breakage

Rods replacement

5

64

Pain

7.8

Nonfusion

Single rod breakage

Rods replacement, satellite rods assistance

6

27

Pain

14.2

Nonfusion

Double rods breakage

Rods replacement, satellite rods assistance

7

30

Pain

16.7

Nonfusion

Double rods breakage

Rods replacement, satellite rods assistance

8

29

Asymptomatic

3.3

Fusion

Single rod breakage

Without revision

TABLE 3 Univariate analysis of the prognostic factors affecting instrumentation survival Factors

No. of all

No. of patients

P (log-rank test)

patients

with instrumentation failure

Sex: male/female

20/10

6/2

0.318

Age: ≤45 years/＞45 years

22/8

7/1

0.298

BMI：≤28/＞28

24/6

4/4

0.011*

Smoker: yes/no

4/26

1/7

0.963

Tumor histology: primary/metastasis

23/7

7/1

0.434

Perioperative radiotherapy: yes/no

10/20

5/3

0.005*

Perioperative chemotherapy: yes/no

4/26

1/7

0.628

Preoperative embolization: yes/no

17/13

6/2

0.375

Vertebrae resected: single/multiple

25/5

7/1

0.564

Location of TES: thoracic/lumbar

21/9

5/3

0.599

TES in junctional region: yes/no

14/16

5/3

0.432

Surgical approach: posterior only/combined

24/6

8/0

0.181

Anterior fixation: yes/no

4/26

0/8

0.218

No. of instrumented vertebrae: ≤4/＞4

24/6

6/2

0.638

Endplate intact: yes/no

23/7

7/1

0.411

Allograft used: yes/no

6/24

2/6

0.620

Position of TMC: upright/ oblique

21/9

3/5

0.004*

*Statistically significant; TES, total en bloc spondylectomy

TABLE 4 Multivariate analysis of the prognostic factors affecting instrumentation survival Factor

HR (95% CI)

P

BMI >28

8.07 (1.55-41.90)

0.013

Perioperative radiotherapy

9.86 (1.61-60.40)

0.013

TMC in oblique position

7.60 (1.35-42.83)

0.022

HR, hazard ratio; CI, confidence interval